pISSN : 2383-6415   eISSN : 2383-6423

Mechanism of Ca²+ Regulation in Osteoblast-like Cells


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INFORMATION : page. 25~41 / 1999 Vol.1 No.1


ABSTRACT

Physiological activity of osteoblast including bone formation is known to be closely related to the increase of intracellular Ca²+ activity ([Ca²+]i) in osteoblast. Ca²+, is an important intracellular messenger in diverse cellular functions, and regulation of its level is mediated by the transmembrane Ca²+, movement via Ca²+channels, Na+ -Ca²+ exchange, and by intracellular Ca²+, movement through the intracellular stores. The purpose of this study is to investigate how the intracellular Ca²+ is regulated in osteoblast-like cells(OLCs) by measuring Ca²+ activity with cell imaging technique. OLCs were isolated from femur and tibia of neonatal rats, and cultured for 7 days. Cultured OLCs were loaded with a Ca²+, -sensitive fluorescent dye, Fura-2, and fluorescence images were monitored with a cooled CCD camera. The images were processed and analyzed with an image analyzing software. The results were as follows. (1) [Ca²+]i of OLC decreased as the Ca²+ concentration in the superfusing Tyrode solution was lowered. When Na+ concentration in the superfusing solution was decreased, [Ca²+]i increased. These suggest that Ca²+ flux occurs via the Na+ -Ca²+ exchange mechanism. (2) When Na+ in the superfusinz solution was removed. a transient Ca²+, increase(Ca²+ spike) was occasionally observed. However, Ca²+ spike was not observed after adding 1 ㎛ thapsigargin, This implies that the generation of Ca²+ spike is mediated by the release of Ca²+ from endoplasmic reticulum(ER). (3) As the ㎛ concentration in the superfusing solution was raised, the frequency of 0mM Na+ -induced Ca²+ . spike increased, suggesting that Ca²+ -induced Ca²+ release(CICR) mechanism exists. (4) After [Ca²+]i was decreased with the superfusion of Ca²+ -free solution containing thapsigargin, the recovery of [Ca²+]i with reperfusion of 2.5mM Ca²+ solution transiently exceeded the control level, suggesting that the depletion of Ca²+ in ER induces Ca²+ influx from extracellular medium via store-operated Ca²+ influx(SOCD mechanism. (5) [Ca²+]i was not affected by the superfusion of 25mM K' Tyrode solution. These results suggest that intracellular Ca²+ activity in osteoblast is regulated by transmembrane Ca²+ flux via Na+ -Ca²+ exchange, Ca²+ release from the internal store (ER) via Ca²+ -induced Ca²+ release. and store- operated Ca²+ influx across the cell membrane.

Keyword :

골아세포,Ca²+ 활성도,Na+-Ca²+ 교환이동,Osteoblast-like cell,Ca²+ activity,Na+-Ca²+ exchange,Ca²+ -induced Ca²+ release,store-operated Ca²+ influx


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